1. Field of the Invention
The present invention relates to a method for searching for a dip angle using a tilt-compensated electronic compass, and more particularly to a method for searching for a dip angle using a tilt-compensated electronic compass, which finds a dip angle suitable for current environments before detecting an azimuth angle, and thereby acquires a more accurate azimuth angle from the electronic compass having a two-axis geomagnetic sensor on the basis of the found dip angle.
2. Description of the Related Art
In recent times, there have been developed small-sized and low-priced geomagnetic sensor modules. With the increasing development of MEMS (Micro-Electro Mechanical Systems) technology, chip-sized geomagnetic sensor modules have been newly developed and used for a variety of applications. However, there is a need for a specific application for preventing the geomagnetic sensor from being horizontally maintained to consider a dip angle (i.e., a magnetic dip angle) corresponding to an inclination angle, resulting in difficulty in calculating a correct azimuth angle using only the two-axis geomagnetic sensor.
Therefore, the above specific application where the geomagnetic sensor is not horizontally maintained must compensate for a tilted or inclined status to provide a horizontal status, and must detect an azimuth angle in the horizontal status. For this purpose, a two-axis geomagnetic sensor and an acceleration sensor for detecting the degree of tilt or inclination must be used at the same time to compensate for an azimuth error by converting a tilted coordinate into a horizontal coordinate.
FIG. 1a is a perspective view illustrating a general three-axis geomagnetic senor and FIG. 1b is a perspective view illustrating a general two-axis geomagnetic sensor.
The three-axis geomagnetic sensor shown in FIG. 1a has a limitation in its installation space, such that it is difficult for the three-axis geomagnetic sensor to be applied to small-sized multimedia devices, etc. Therefore, there have been recently developed and investigated a variety of methods for compensating for the tilted coordinate using the two-axis geomagnetic sensor shown in FIG. 1b. 
FIG. 2 is a block diagram illustrating a two-axis geomagnetic sensor for use in a conventional electronic compass.
Referring to FIG. 2, the two-axis geomagnetic sensor for use in the conventional electronic compass includes a geomagnetic sensor 21 for detecting a geomagnetic azimuth angle; an acceleration sensor 22 for detecting a tilted geomagnetic angle on the basis of the horizon; an analog processor 23 for amplifying signals detected by the sensors 21 and 22, and filtering the amplified signals; an analog/digital (A/D) converter 24 for converting the output signal of the analog processor 23 into a digital signal; and a digital processor 25 for calculating a geomagnetic azimuth angle on the basis of the digital signal received from the A/D converter 24.
In this case, the geomagnetic sensor 21 is a prescribed sensor for detecting/measuring the earth's magnetic field intensity, and includes x-axis, and y-axis sensors arranged at right angles to each other.
A method for compensating for the tilted angle in the above-identified conventional electronic compass will hereinafter be described.
The conventional electronic compass must compensate for the tilted coordinate to be changed to the horizontal coordinate using the following Equation 1 serving as a coordinate conversion equation between the tilted coordinate and the horizontal coordinate and the following Equation 2 serving as a coordinate conventions matrix.
FIG. 3a is a conceptual diagram illustrating the relationship between the horizontal coordinate and the tilted coordinate. Referring to FIG. 3a, “θ” is a tilted angle of the x-axis of the horizontal coordinate, and “φ” is a tilted angle of the y-axis of the horizontal coordinate. “Xh”, “Yh”, and “Zh” are individual values of the horizontal coordinate, and “Xmc”, “Ymc”, and “Zmc” are individual values of the tilted coordinate.                               [                                                    Xh                                                                    Yh                                                                    Zh                                              ]                =                              C            b            h                    ⁡                      [                                                            Xmc                                                                              Ymc                                                                              Zmc                                                      ]                                              [                  Equation          ⁢                                          ⁢          1                ]                                          C          b          h                =                  [                                                                      cos                  ⁢                                                                          ⁢                  θ                                                                              sin                  ⁢                                                                          ⁢                  θ                  ⁢                                                                          ⁢                  sin                  ⁢                                                                          ⁢                  ϕ                                                                              sin                  ⁢                                                                          ⁢                  θ                  ⁢                                                                          ⁢                  cos                  ⁢                                                                          ⁢                  ϕ                                                                                    0                                                              cos                  ⁢                                                                          ⁢                  ψ                                                                                                  -                    sin                                    ⁢                                                                          ⁢                  ϕ                                                                                                                          -                    sin                                    ⁢                                                                          ⁢                  θ                                                                              cos                  ⁢                                                                          ⁢                  θ                  ⁢                                                                          ⁢                  sin                  ⁢                                                                          ⁢                  ϕ                                                                              cos                  ⁢                                                                          ⁢                  θ                  ⁢                                                                          ⁢                  cos                  ⁢                                                                          ⁢                  ϕ                                                              ]                                    [                  Equation          ⁢                                          ⁢          2                ]            
The following Equation 3 is adapted to calculate an the azimuth angle “Ψ”. The “Xmc”, “Ymc”, and “Zmc” values and the “θ” and “φ” angles are needed to calculate the azimuth angle “Ψ”. The “θ” and “φ” angles are detected by a two-axis acceleration sensor, and the “Xmc” and “Ymc” values are detected by a two-axis geomagnetic sensor, however, the above two-axis sensors cannot calculate the “Zmc” value.                               ψ          -                                    tan                              -                1                                      ⁡                          (                              Yh                Xh                            )                                      =                              tan                          -              1                                ⁡                      (                                                                                                      -                      Ymc                                        ·                    cos                                    ⁢                                                                          ⁢                  ϕ                                +                                                      Zmc                    ·                    sin                                    ⁢                                                                          ⁢                  ϕ                                                                                                  Xmc                    ·                    cos                                    ⁢                                                                          ⁢                  θ                                +                                                      Ymc                    ·                    sin                                    ⁢                                                                          ⁢                  θ                  ⁢                                                                          ⁢                  sin                  ⁢                                                                          ⁢                  ϕ                                +                                                      Zmc                    ·                    sin                                    ⁢                                                                          ⁢                  θ                  ⁢                                                                          ⁢                  cos                  ⁢                                                                          ⁢                  ϕ                                                      )                                              [                  Equation          ⁢                                          ⁢          3                ]            
The following Equation 4 describes the “θ” and “φ” angles detected by the acceleration sensor.φ=sin−1(ax/g)θ=sin−1(ay/g)  [Equation 4]
With reference to the above Equation 4, “g” is acceleration due to gravity, “ax” is an x-axis component of the acceleration sensor, and “ay” is a y-axis component of the acceleration sensor.
The following Equation 5 is acquired from the aforementioned Equations 2 and 3, and requires a specific value “Zh” to obtain the “Zmc” value using the above Equation 5.                     Zmc        =                              Zh            +                                          Xmc                ·                sin                            ⁢                                                          ⁢              θ                        -                                          Ymc                ·                sin                            ⁢                                                          ⁢              ϕ              ⁢                                                          ⁢              cos              ⁢                                                          ⁢              θ                                            cos            ⁢                                                  ⁢            ϕ            ⁢                                                  ⁢            cos            ⁢                                                  ⁢            θ                                              [                  Equation          ⁢                                          ⁢          5                ]            
FIG. 3b is a conceptual diagram illustrating the relationship between the geomagnetic field and the horizontal coordinate. Referring to FIG. 3b, “Xh”, “Yh”, and “Zh” are individual values of the horizontal coordinate, “Xd”, “Yd”, and “Zd” are individual values of the geomagnetic field, “Nm” is magnetic north, and “λ” is a specific angle (i.e., a dip angle) made between the geomagnetic field and the horizontal coordinate.
The following Equation 6 is adapted to describe the relationship between the geomagnetic field and the horizontal coordinate. The following Equation 7 is adapted to describe a reference coordinate of the geomagnetic field. The following Equation 8 is acquired from the above Equations 6 and 7.                               [                                                    Xd                                                                    Yd                                                                    Zd                                              ]                =                              [                                                                                cos                    ⁢                                                                                  ⁢                    λ                                                                    0                                                                      sin                    ⁢                                                                                  ⁢                    λ                                                                                                0                                                  0                                                  0                                                                                                                        -                      sin                                        ⁢                                                                                  ⁢                    λ                                                                    0                                                                      cos                    ⁢                                                                                  ⁢                    λ                                                                        ]                    ⁢                                          [                                                    Xh                                                                    Yh                                                                    Zh                                              ]                                    [                  Equation          ⁢                                          ⁢          6                ]                                          [                                                    Xd                                                                    Yd                                                                    Zd                                              ]                =                  [                                                    1                                                                    0                                                                    0                                              ]                                    [                  Equation          ⁢                                          ⁢          7                ]            Zh=sinλ  [Equation 8]
Provided that the “λ” value is recognized, the “Zmc” value can be calculated by the above Equations 5 and 8, and a tilt-compensated azimuth angle can also be calculated using only the two-axis geomagnetic sensor.
The above-identified conventional method calculates the azimuth angle using the dip angle “λ” predetermined experimentally, such that it can substitute for the three-axis geomagnetic sensor.
However, the aforementioned method has a disadvantage in that it cannot consider the fact that a dip angle created indoors is different from the other dip angle created outdoors within the range of a specific area having the same dip angle, such that the scope range of an error rate of the dip angle is set to ±6.0 according to the azimuth angle as shown in FIG. 4, resulting in deteriorated accuracy in response to the influence of peripheral magnetic substances.